344bac8f0d
Move mnt->mnt_node into the union with mnt->mnt_rcu and mnt->mnt_llist
instead of keeping it with mnt->mnt_list. This allows us to use
RB_CLEAR_NODE(&mnt->mnt_node) in umount_tree() as well as
list_empty(&mnt->mnt_node). That in turn allows us to remove MNT_ONRB.
This also fixes the bug reported in [1] where seemingly MNT_ONRB wasn't
set in @mnt->mnt_flags even though the mount was present in the mount
rbtree of the mount namespace.
The root cause is the following race. When a btrfs subvolume is mounted
a temporary mount is created:
btrfs_get_tree_subvol()
{
mnt = fc_mount()
// Register the newly allocated mount with sb->mounts:
lock_mount_hash();
list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts);
unlock_mount_hash();
}
and registered on sb->s_mounts. Later it is added to an anonymous mount
namespace via mount_subvol():
-> mount_subvol()
-> mount_subtree()
-> alloc_mnt_ns()
mnt_add_to_ns()
vfs_path_lookup()
put_mnt_ns()
The mnt_add_to_ns() call raises MNT_ONRB in @mnt->mnt_flags. If someone
concurrently does a ro remount:
reconfigure_super()
-> sb_prepare_remount_readonly()
{
list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
}
all mounts registered in sb->s_mounts are visited and first
MNT_WRITE_HOLD is raised, then MNT_READONLY is raised, and finally
MNT_WRITE_HOLD is removed again.
The flag modification for MNT_WRITE_HOLD/MNT_READONLY and MNT_ONRB race
so MNT_ONRB might be lost.
Fixes:
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| .. | ||
| acpi | ||
| asm-generic | ||
| clocksource | ||
| crypto | ||
| cxl | ||
| drm | ||
| dt-bindings | ||
| keys | ||
| kunit | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
| rv | ||
| scsi | ||
| soc | ||
| sound | ||
| target | ||
| trace | ||
| uapi | ||
| ufs | ||
| vdso | ||
| video | ||
| xen | ||